Mark Wahlberg telling Prime, "This isn't you," gives us the idea that the good robot is longer an ally. The official synopsis simply says that "humans are at war with the Transformers, and Optimus Prime is gone."
We also get glimpses of Dragonstorm flying over the coast of England, Transformers fighting Nazis, and the relatively petite robot named Cogman that a stunned Wahlberg calls "you crazy ninja butler," after he ably crushes an opponent about 10 times his size.
Per ScreenRant, Cogman is "a centuries-old man servant who happens to have anger issues, among other things." So that makes him the angry steampunk C3PO.
The movie, which also stars Stanley Tucci, Josh Duhamel, Tyrese Gibson, John Turturro and Anthony Hopkins, opens June 21.